The field of the invention is acetylenically unsaturated, polyhydroxy, acyclic, organic compounds and the invention is particularly concerned with the regeneration of copper catalysts used in suspended form for the production of butynediol from acetylene and formaldehyde.
The state of the art of butynediol (2-butyne-1,4-diol) production and the catalysts used therein may be ascertained by reference to the Kirk-Othmer, "Encyclopedia of Chemical Technology", 2nd Edition, Vol. 1 (1963) pp. 502-611; U.S. Pat. Nos. 3,920,759; 3,954,669; 4,067,914; 4,119,790; and 4,127,734; and West German Published Applications 2,206,693 and 2,602,418, the disclosures of which are incorporated herein.
Besides the main component copper, used in the butynediol production, the catalysts also may contain other metals such as chromium, silver, bismuth and cobalt. As a rule, a copper/bismuth catalyst is used. For safety reasons, and in view of reaction engineering requirements, the catalysts are used in the form of carrier catalysts. Appropriate carrier materials are silicates and oxides such as magnesium silicate, pumice, silica gel, kieselguhr, silicon dioxide, magnesium dioxide, barium oxide, calcium oxide and aluminum oxide. For practical considerations, silicates and aluminum oxide are preferred.
The conversion of the catalysts into the catalytically active form can be carried out as described in West German Published Application 26 02 418 and U.S. Pat. Nos. 4,067,914; 3,920,759 and 3,954,669.
These catalysts suspended in the reaction medium for the production of butynediol lose their activity with time, and furthermore their separation from the reaction mixture becomes more difficult as the catalysts age. When filters are employed a significant drop in filtering capability is observed.
This loss in activity of the catalysts is attributed essentially to a deposition of carbon compounds on the active centers, for instance the formation of cuprene during the reaction. It is therefore necessary to remove in a continuous or a discontinuous manner, the used catalyst from the reactors and to replace the used catalyst with a fresh one.
U.S. Pat. No. 4,119,790 discloses a continuous, multi-stage, low pressure ethynylation process for the production of butynediol. The steps of the process include:
(a) continuously reacting formaldehyde and acetylene in a first stage reaction zone at a partial pressure of acetylene of less than 2 atmospheres and a reaction temperature of about 80.degree. to about 105.degree. C., in a stirred aqueous medium, in the presence of an ethynylation catalyst slurry consisting essentially of a finely divided water-insoluble complex cuprous acetylide powder made from a catalyst precursor material containing greater than 20% and less than 35% by weight of copper, 0 to about 3%, and preferably 2-3% by weight of bismuth on a magnesium silicate carrier therefor, to form a first stage reaction product containing butynediol;
(b) continuously withdrawing the first stage reaction product and the catalyst slurry as a first stage effluent;
(c) continuously passing the first stage effluent into a second stage reaction zone into which additional acetylene is being supplied;
(d) repeating steps (b) and (c), if desired, to other additional stage reaction zones to produce a final stage effluent;
(e) continuously withdrawing the final stage effluent;
(f) continuously separating the final stage effluent by adding into catalyst-free liquid containing the butynediol and a concentrated catalyst slurry; and
(g) continuously recycling the concentrated catalyst slurry to the first reaction zone.
The regeneration of old catalyst is generally known. West German Published Application 22 06 693 emphasizes the simple regeneration of the suspended catalyst with respect to the formed catalyst as mounted in a solid bed (Column 2, lines 34 through 41) specifically for the production of butynediol in the presence of copper carrier catalysts.
A specific proportion of the catalyst suspended in the reaction medium is continuously removed by a sludge centrifuge and washed several times with water and regenerated by dissolving the metals in nitric acid and by the ensuing step of precipitation, and then the regenerated catalyst is fed in the form of a pumpable suspension back into the reactor (Column 4, last paragraph).
On the one hand this process is relatively costly in view of the many steps required, and on the other hand the application of nitric acid places high requirements on the materials of the regeneration apparatus. This process further suffers from the drawback that operating with nitric acid may cause health problems.